The NCAA NET Rankings Explained
It's the most important metric in college basketball, and most fans have no clue what it is.
Starting in the 2018-19, the NCAA made one of the best decisions the hapless governing body had made in recent memory. The antiquated RPI was replaced with the NET ranking to more accurately rank teams heading into the March Madness tournament. After a few seasons of use, many fans still don't completely understand what it measures and, maybe most importantly, why it measures those things. But with a little bit of simple math fans can easily understand how their team ranks nationally and what the March Madness committee will be looking at prior to Selection Sunday. Let's take a look!
...Oh wait, did that above paragraph seem too good to be true? Well that's because it is. We'll cover that later...
The NET ranking previously took into account five measurements:
1. Team Value Index"
2. Net Efficiency
3. Winning Percentage
4. Adjusted Win Percentage
5. Scoring Margin
Just before the 2020 season, however, the NCAA simplified this due to some pretty glaring issues. First off, the whole genesis of NET was because the previous metric, RPI, was solely based on winning percentages. Therefor, teams that played easier schedules or played in lower level conferences had a monster advantage. On the flip side, remember all those years the Virginia Tech got snubbed from the NCAA tournament? Former coach Seth Greenberg after the Hokies got their hearts ripped out by Tyler Hansbrough and UNC in the 2008 ACC tournament said if the Committee didn't invite the Hokies to March Madness they were "certifiably insane". He was right. The issue? The Hokies had an RPI ranking of 63, which was just outside the accepted limit at the time for bubble teams. The Hokies were penalized for being in the toughest conference in America.
So, the NCAA got rid of classic winning percentage and adjusted winning percentage metrics in their calculation. At least at the surface level.
The move was also made to get rid of Scoring Margin. There are multiple reasons why you wouldn't want to bother with scoring margin in any sort of statistical measurement, but the main reason was it rewarded teams for running up the score on lesser opponents. From a competition perspective, no one wants that. Every major college basketball programs schedules 5-6 complete cupcake games a season to get into the flow of things, and the NCAA knows this. It's financially important for mid and low major programs to schedule these games. No one wants to see a team schedule more of these games than needed and score 100+ every time, however.
Another reason to remove Scoring Margin was the NCAA's weird quirk on capping the measurement. A team couldn't have a scoring margin for a game greater than +/- 10 points. Also, a game that went into overtime couldn't result in a scoring margin +/- 1 point. This, obviously, renders the purpose of looking at scoring margin useless.
For the 2021 season, only two variables are being used to measure NET:
1. "Team Value Index"
2. Adjusted Net Efficiency
It's All About Efficiency
At its core, the NET metric is all about measuring efficiency. The best way to think about efficiency in sports is, "How regularly does this team succeed at what they want to do during a game?" Pure efficiency in basketball terms comes down to points per possession.
- Offensive Efficiency = total points scored / total number of offensive possessions
- Defensive Efficiency = total points allowed / total number of defensive possessions
- Net Efficiency = Offensive Efficiency - Defensive Efficiency
Obviously, you want a higher Offensive Efficiency and a lower Defensive Efficiency in order to maximize Net Efficiency. This is where style of play comes into the conversation. To explain this let's look at two examples that are stark differences: Villanova and Memphis.
Villanova runs a slow, methodical offense (similar to the Hokies, actually) that focuses on heavy passing to create open shots later in the shot clock. As a result, Villanova is only averaging 67.3 offensive possessions per game this season, which is ranked #312 out of 353. Villanova counters this by taking open shots and making them. Villanova scores 1.163 points per possession (Offensive Efficiency) which ranks #7 nationally and results in 78.2 points per game which ranks #44 nationally.
Memphis, on the other hand, plays at a lightning fast pace and takes lots of shots off of isolation offensive sets. Memphis averages a whopping 77.6 offensive possessions per game, ranked #9 nationally. The issue for Memphis is they have trouble making those tough shots, so they only score 0.988 points per possession (Offensive Efficiency) which ranks #168 nationally and results in 76.6 points per game which ranks #58 nationally.
Even though Memphis is the more talented team by most everyone's standards, they don't succeed offensively at a rate even close to what Villanova does. And it shows in the wins and losses. Villanova is 7-2 even after playin 3 top 20 teams, while Memphis is 5-3 and has played no nationally ranked teams.
Defensive Efficiency is more cut and dry. By taking the difference between Offensive Efficiency and Defensive Efficiency you can pretty accurately understand how "good" a team is.
The NET takes this a step further and creates an opponent adjusted efficiency metric. To make a pure efficiency metric "opponent adjusted", the NCAA takes into account game location (home vs road vs neutral) as well as opponent strength. The Opponent Strength variable is measured using the "Team Value Index" measurement.
"Team Value Index"
"Team Value Index" is a wins and losses based measurement that takes into account opponents played, location, and who the winner was of those matchups. It's purpose is two fold: to provide context for the adjusted efficiency and to stand alone as its own team ranking system.
Remember when I said that the NET ranking was too good to be true? This is where it happens.
We don't know how "Team Value Index" is calculated. According to the NCAA, it is an "Algorithm set up to reward teams who beat other good teams." Per their official release May 12, 2020, the NCAA worked with Google Cloud Professional Services to develop and alter NET. The NCAA has been asked about releasing the calculation used, but it remains a closely guarded secret between the NCAA and Google. Most likely, this is due to the private partnership with Google.
It's a big miss by the NCAA. There's no reason to develop a complex algorithm with the help of Google and keep it from the fans and programs. The only conceivable reason for this would be so programs don't take advantage of the metric via scheduling like they did with the RPI and original NET metrics.
We can only speculate on how the "Team Value Index" is calculated. My personal best guess is a jacked up version of variables #3-5 of the original net rankings. By taking into account scoring margin, winning percentage, and some more advanced metrics such as tempo/game control and luck factors, you could calculate a measurement that would both rank teams and also act as a multiplier for the adjusted efficiency metrics. It would look something like this:
Team Value Index = (Scoring Margin/100) + Winning Percentage + Game Control metric - Luck Metric
Those game control and luck metrics could mirror what we see from highly regarded statistician (and Hokie legend) Ken Pomeroy or could be entirely different, we don't know. But we can take our best guess at how teams would look. For example, a team like Villanova who controls the pace of play, takes open shots, makes said shots, and has most losses due to factors like foul trouble and teams shooting the ball at a better rate than usual would have a decent scoring margin, high winning percentage, high game control, and would have a lower metric for luck.
It's disappointing that we don't know these things exactly, but the NCAA is incapable of doing things correctly. All we can really do is guess and react.
The Quads System
Now that we (kind of) understand how NET is calculated we can move to how the rankings are grouped. All 328 teams are put into quads based on their NET ranking (which updates regularly throughout the season). Every win/loss is either a Quadrant 1, 2, 3, or 4 result. Much like the adjusted net efficiency metrics, these are based heavily on game location. Here's how the quads break down based upon where your team plays the game:
- Quadrant 1: Home 1-30, Neutral 1-50, Away 1-75
- Quadrant 2: Home 31-75, Neutral 51-100, Away 76-135
- Quadrant 3: Home 76-160, Neutral 101-200, Away 135-240
- Quadrant 4: Home 161-353, Neutral 201-353, Away 241-353
Describing teams by their record vs individual quadrants is the easiest way to compare teams. This makes it easy to see which teams play tougher schedules, too, which is key in the NCAA's move to go away from programs scheduling too many cupcake games.
How The Hokies Look in NET So Far
You can look at the NET Rankings as they update throughout the season. As of this publication date (December 10, 2021), the Hokies are #36 in the NET Rankings. Here are the results: